Resource Ecology and Ecosystem Modeling Program
Fish Stomach Collection and Lab Analysis
During the third quarter of 2012, Resource Ecology and Ecosystem Modeling (REEM) program staff analyzed the contents of 2,014 groundfish stomachs in the laboratory and participated in 10 legs of the summer groundfish surveys. Five predator species were analyzed from the eastern Bering Sea, and Pacific halibut were analyzed from the Gulf of Alaska. This resulted in 8,801 records being added to the AFSC Groundfish Food Habits database. In preparation for stable isotope analysis, approximately 200 muscle and liver tissue samples from Alaskan groundfish were tinned in preparation for gas isotope-ratio mass spectroscopy. Groundfish stomach samples were collected during AFSC surveys of the eastern Bering Sea continental shelf and slope, and the Aleutian Islands region. Stomach samples also were collected during cooperative surveys of demersal and epipelagic waters of the Chukchi Sea. During fisheries operations in the eastern Bering Sea, fishery observers collected stomach samples from 68 arrowtooth flounder, 828 walleye pollock, and 1 Pacific cod.
By Troy Buckley, Geoff Lang, Mei-Sun Yang, Richard Hibpshman, Kimberly Sawyer, Caroline Robinson and Sean Rohan
Eastern Bering Sea Continental Shelf and Slope Groundfish Surveys
Large and abundant predators were the focus of this year’s stomach sample collection from the eastern Bering Sea bottom trawl surveys of the continental shelf and slope. In total, 1,498 stomach samples were collected during the survey of the eastern Bering Sea slope, and 5,260 stomach samples were collected during the survey of the eastern Bering Sea shelf. A fairly high number of samples from Pacific cod, walleye pollock, arrowtooth flounder, Kamchatka flounder, Greenland turbot, and Bering skate were collected from both surveys. Pacific halibut, flathead sole, and Bering flounder were only collected during the shelf survey. Nine additional skate species were collected mostly in one survey or the other (or only rarely) depending on their distribution (or abundance). Combined, these predators account for a large portion of the post-larval predation mortality on many commercially important species of fish and crab in the eastern Bering Sea.
Two pairs of congeneric flatfish species – Kamchatka flounder and arrowtooth flounder, and Bering flounder and flathead sole – have a high degree of overlap in their pair-respective morphology, geographic distribution, and food habits. Thus, each pair is collected as a unit, but analyses of the stomach contents and entry into the database are species specific. Congeneric species of skates display more distinction in their geographic and depth distribution, and their food habits differ somewhat due to differences in body size and available prey within their distributions. In addition to providing current information on predation mortality and energy transfer through the eastern Bering Sea foodweb, these samples will provide additional ecological information on the differences in food habits among closely related species.
By Troy Buckley and Sean Rohan
Aleutian Islands Groundfish Survey
Staff with the REEM program participated in the 2012 Aleutian Islands bottom trawl survey. Staff on board the chartered fishing vessels Sea Storm and Ocean Explorer conducted 4,018 stomach scan analyses from 19 marine fish species: walleye pollock, Pacific cod, arrowtooth flounder, Pacific halibut, Kamchatka flounder, Atka mackerel, blackspotted rockfish, flathead sole, northern rockfish, northern rock sole, Pacific ocean perch, southern rock sole, shortspine thornyhead, yellow Irish lord, Bathylagidae, myctophids, squids, red-bended rockfish, and armorhead sculpin. This year we aimed to get 100% identification of the prey fish to species level through on-deck examination, lab identification, and genetic identification, when necessary. Therefore, all unidentified prey fish found in the stomachs on board were frozen and brought back to the lab for identification.
By Mei-Sun Yang, Troy Buckley, Geoff Lang, Richard Hibpshman, Kimberly Sawyer, and Caroline Robinson
Arctic Ecosystem Integrated Survey
From 12 August to 24 September REEM personnel participated in the AFSC’s bottom trawl survey of the eastern Chukchi Sea aboard the chartered fishing vessel Alaska Knight. Scientific trawling operations were performed at stations uniformly located across the continental shelf of the eastern Chukchi Sea between the Bering Strait and Pt. Barrow, within the U.S. Exclusive Economic Zone. At each sampling station after standard catch processing, stomach samples were collected from selected fish species present in the catch and were preserved for analysis to be performed later in the Food Habits Lab at the AFSC. The sampling strategy was designed to include all species of fish that might be encountered, but with added emphasis on more abundant or larger-mouthed species. A total of 1,930 stomachs were collected from 38 species of fish, including Arctic cod, saffron cod, Arctic staghorn sculpin, and Bering flounder. For many species, the number of samples collected was low due to small catches or infrequent capture. However, about 75% of the species we sampled during this survey were also collected during the 2010 survey of Norton Sound and the northern Bering Sea and these samples may provide supplemental information about the food habits of the same species inhabiting the Chukchi Sea. The stomach contents data from the Chukchi Sea specimens, along with the survey catch data, will be used to expand existing information about food habits and predator-prey relationships as well as update existing food web models of the Alaskan Arctic.
By Andy Whitehouse and Troy Buckley